Influencing Factors of Hydration Number of Synthesized Methane Hydrates in Sediment

The low-field NMR method is introduced to explore the effect of various experimental conditions on hydration number during hydrate dissociation in methane hydrate-bearing sediments. It is shown that the NMR signal peak value of water is independent of the dry density of sediment, gas pressure, and salt concentration and significantly influenced by temperature. A relationship among NMR signal peak value, substance content, pressure, and temperature is developed to estimate the hydration number of pore hydrates during hydrate dissociation. It is revealed that the hydration number (Nh) of synthesized methane hydrates remains practically unchanged during hydrate dissociation in fine-grained sediments and is trivially influenced by experimental conditions, including initial pressure, density, initial water saturation, and salt content. Our experimental results indicated that the hydration number of methane hydrates is about 6.5, which is slightly higher than that of natural hydrates.